Our studies of the human erythrocyte membrane proteins will continue to emphasize investigation of the transmembrane proteins. The human erythrocyte has two groups of such proteins: (a) the sialoglycoproteins (SGP), and (b) those glycoproteins which do not contain sialic acid. Protein 3, the major membrane protein of the red cell which contains about 10% carbohydrate but little sialic acid, is an example of the latter group. The oligosaccharide chains of these proteins terminate for the most part with a galactose residue. The organization of the transmembrane proteins and their relationship to function of the red cell will continue to be the focus of our studies. In order to relate the cell morphology with the molecular organization, the freeze-fracture technique, which allows us to isolate the outer half of the membrane bilayer, will be used in conjunction with vectorial membrane probes and hydrolases (both proteases and glycosidases) to identify the membrane particle observed in freeze fracture.